Non Thermal Plasma NO_x Remediation: From Binary Gas Mixture to Lean-Burn Gasoline and Diesel Engine Exhaust

Author： Khacef A. Cormier J. M. Pouvesle J. M.

Publisher： Science and Technology Network Inc.

ISSN： 1203-8407

Source： Journal of Advanced Oxidation Technologies, Vol.8, Iss.2, 2005-07, pp. : 150-157

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Abstract

Experiments are presented on the plasma removal of NO_x (sum of NO and NO₂ concentrations) and hydrocarbons in atmospheric pressure gas streams by sub-microsecond pulsed dielectric barrier discharge processing. This investigation presents the effects of electrical input energy, hydrocarbon addition, and water addition on the NO_x chemistry and by-products formation. Exhaust gas mixtures with composition containing up to seven gases (CO, CO₂, NO, O₂, H₂O, C₃H₆, N₂) were synthesized. The objective is to use synthetic gas exhaust simulating diesel and Lean Bum gasoline engine exhaust with propene as a reductant agent. It was established that the observed chemistry in the plasma includes conversion of NO to NO₂ as well as the partial oxidation of hydrocarbon. In a given reactor under identical gas composition and equivalent energy density deposition, experimental results show that the main parameter which controls the efficiency of the plasma process is the energy deposition mode. The best results on NO_x and hydrocarbon removal efficiencies have been obtained at low input energy per pulse and high discharge frequency. NO_x removal improves with increasing input energy deposition and the presence of water in the gas mixture appears to essentially enhance the chemistry process efficiency, reducing by this way the energy cost of the processes. For example, for an input energy density of 27 J/L, the fraction of NO_x removed was about 60% with an energy cost less than 30 eV/molecule in the case of simulated diesel engine exhaust. The data obtained suggest that aldehydes (CH₂O and CH₃CHO) are formed in concert with NO oxidation to NO₂ in the plasma phase. Methyl nitrate (CH₃ONO₂) and nitromethane (CH₃NO₂) are the main R-NO_x compounds produced and small amounts of nitrous acid (HNO₂) and formic acid (CH₂O₂) were also detected.